In this type of the conventional machine, the upper assembly structure comprises a swivel deck body mounted on a propelling apparatus to swivel about a vertical axis, an engine mounted rearwardly of the swivel deck body, an oil tank and a fuel tank arranged at the right side of the swivel deck body, the engine and the tanks being covered at peripheries thereof, a driver's seat mounted at a side of the tank forwardly and upwardly of the engine, a rear cover member for covering an engine compartment housing the engine, a cover member for covering a tank compartment housing the oil tank, and a support frame mounted at a rear portion of the swivel deck body to extend across the engine for supporting the cover members and a protection device such as a cabin or a ROPS covering the driver's seat (see Japanese Unexamined Patent Application Publication No. 2003-64724).
The support frame includes a backbone member provided above the engine, a pair of right and left front leg members and a pair of right and left rear leg members extending downward from the backbone member at front and rear portions thereof to support the rear cover member and the protection device.